American heavyweight prospect Deontay Wilder promised to fight a fan if he reached 5,000 likes on social networking site Facebook.

The 29-year-old, who is undefeated after 32 fights and set to face Bermane Stiverne for the WBC world title in January, kept his promise in an amusing YouTube video.

Having knocked out an internet troll in real life back in May (video below), this time the Alabama fighter, winner of Olympic bronze in 2008, took a more humorous approach, lacing up his gloves to punch a fan.

Back in May, his fight with an internet troll was rather more serious.

Charlie Zelenoff had subjected Wilder to years of abuse over social media even going as far as to say he was going to and tape his daughter's mouth.

"He said he was going to murder me," Wilder told TMZ at the time. "He said he was going to tape my daughter's mouth ... when dealing with my kids, that's below the belt. That's what really got me."

Wilder accepted Zelenoff's challenge to a fight, met him in a Los Angeles gym and knocked him out.

Wilder said: "I genuinely care for the guy. I want him to stop [harassing people] before he messes with the wrong person. You never know who you're dealing with."